The quest for new zeolitic materials has recently focused on the design of new organoammonium templates, i.e. structure directing agents (SDA), often expensive and complicated molecules that impart aspects of their structural features to the zeolite to yield a desirable pore structure. See, e.g. A. Corma et al, Nature 418 (2002) pp. 514-517; P. Wagner et al, Chem. Comm. (1997) 2179-2180; U.S. Pat. Nos. 5,489,424 and 6,632,417 B2. With goals of designing spatial features such as large pores or intersecting channels within the zeolite, many of these organoammonium SDA's are necessarily large molecules of low charge density and have thus been accompanied by a focus on low charge density (i.e., high silica) frameworks. It would be economically advantageous to use commercially available organoammonium SDAs to synthesize new zeolites. A potential way to use commercially available SDA is to use two or more templates to form a single structure. This approach, however, would likely fail at high Si/Al ratios, because each template will be present in large excess relative to the framework charge to be balanced, each leading to its own product. Low Si/Al ratios present a better situation to pursue template cooperation because there is more framework charge to balance, allowing more reasonable template/Al ratios.
Low Si/Al (Si/Al<10) ratio chemistry has traditionally been carried out in a gel phase dominated by the significant presence of alkali cations, which play an important role in structure direction. Low Si/Al ratio organoammonium-based aluminosilicate reaction mixtures are known to form solutions rather than gels like their alkali-based analogs see, R. F. Mortlock et al, J. Phys. Chem. 95 (1991) 372-378. This is a matter of solubility as the high charge density on aluminosilicate solution species are not predisposed to form a gel network with the low charge density organoammonium cations. This Charge Density Mismatch (CDM) also leads to difficulty in zeolite crystallization, because of the enormous spatial requirements for the number of low charge density organoammonium cations to be accommodated in the pores of a high charge density framework. Applicants have found that adding controlled amounts of at least one second template with a better match in charge density to the CDM aluminosilicate reaction mixture will induce crystallization of an aluminosilicate composition via a cooperative interaction between the templates.
Thus, applicants have developed a process for synthesizing aluminosilicate compositions which comprises purposely forming a fully reactive aluminosilicate reaction mixture, which cannot crystallize, followed by a perturbation of the reaction mixture via the addition of controlled amounts of additional templating agents (organic cations, alkali/alkaline earth cations, or mixtures thereof) which induce crystallization of a zeolite or layered aluminosilicate via a cooperative interaction between the templates. In a preferred embodiment, the process involves preparing a first solution comprising sources of aluminum, silicon, optionally E metals such as gallium, and one organic templating agent in the hydroxide form. This first solution is characterized in that at reaction conditions crystalline aluminosilicate compositions will not crystallize. Adding to the reaction mixture a solution comprising a crystallization inducing templating agent selected from the group consisting of an organic cation (different from the first organic cation) an alkali and/or alkaline earth metal cation and mixtures thereof to form a reaction mixture which is reacted at crystallization conditions to form the a crystalline aluminosilicate composition.